Engine - Overview - Cooper (w10) & Cooper S (w11) MINI Cooper S I

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In 1996 BMW Group and Chrysler entered into a joint venture to design and construct a small gasoline engine with a cylinder displacement of 1598cc. The venture would provide an engine suitable for both car manufacturers in terms of power output and compliance with world emissions. The venture is known by on of the following names

Pentagon or Trident. In addition BMW required a high power derivative for the MINI COOPER S.

The MINI COOPER (COOPER S) engines are a product of this venture.

The MINI COOPER (COOPER S) is a front wheel drive vehicle with the engine mounted transversely across the car.

Engine Derivatives

ENGINE DERIVATIVES

Engine Construction

The engine block and bearing ladder are constructed from cast iron with an aluminum alloy cylinder head. The oil pan is manufactured from aluminum alloy to reduce weight. Despite the iron block and bearing ladder, the engine is very light (129.22 kg.). Main features of the engine include

1. 16 valves, single overhead chain driven camshaft
2. Hydraulic Lifters
3. Automatic adjusting accessory drive belt
4. Supercharger on MINI COOPER S

Engine Block

The engine block is manufactured in two halves from sand cast nodular iron. The top portion (main cylinder block) includes the cylinder bores and has provisions for five main bearing top shells. The lower portion (support ladder) incorporates the lower main bearing shells and support for the rear main oil seal. The engine block and ladder are machined as a matched pair and are not serviced as individual components. Three locating dowels are used to ensure perfect alignment between the support ladder and the engine block.

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A number is stamped on the engine block and the same number is stamped on the bearing ladder. This ensures that the matched pair of components remain together during engine assembly. The other number stamped on the block is the engine plant serial number.

Crankshaft Assembly

The MINI COOPER crankshaft is machined from nodular cast iron. The MINI COOPER S crankshaft is machined from forged steel. Both crankshafts provide a mounting point for the crankshaft sensor reluctor ring that is retained by three bolts. The drive for the oil pump is provided by machined flats towards the front of the crankshaft. The auxiliary drive belt pulley is a press fit on the crankshaft and retained by a bolt.

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Crankshaft Bearings

All MINI COOPER engines use five main bearings. Lubrication is supplied through holes in the upper shell directly from the main oil gallery. The upper shell is grooved to transport oil to the lower plain shells located in the bearing ladder. A thrust washer built into the center upper main bearing shell controls crankshaft end float.

The connecting rod and main bearing shells are made of an aluminum base that is rolled onto a low carbon steel backing.

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MINI COOPER connecting rods are manufactured from 'non-coplanar' powder metal.

They are manufactured in one piece and then fractured across the big end journal.

The MINI COOPER S connecting Rods are manufactured from forged steel to provide additional strength and are fractured.

The big end bearings are of a conventional plain shell design with oil supplied from a hole in the crankshaft.

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Fracture Process

In the fracture splitting process, the connecting rod and big end bearing cap are designed to separate close to the theoretical center line with no loss of material. This is achieved by applying a load between the big end bearing cap and the connecting rod via a wedge in a split mandrel. The big end bore in the connecting rod is pre machined with a notch introduced at the required joint plane to initiate the fracture. The separation is accurately determined by careful consideration of the geometry of the forging and material selection. Fracturing of the connecting rod takes place immediately before the bolts are fitted and correctly tightened, this keeps the matching cap and connecting rod together for subsequent finish machining of the bore.

After fracturing, the surfaces form a unique "multifaceted" joint which provides a contact area much greater than that of a normally ground surface. The multifaceted joint also promotes precise mating between the big end cap and the connecting rod. No further machining of the faces is required, and no additional means of big end bearing to connecting rod location is necessary.

The main benefits of the Fracturing Process are

1. Reduction in manufacturing time and cost
2. Each rod and bearing cap have a unique fracture reducing the possibility of mismatched pairs
3. Improve rod weight control

Pistons

The pistons are of aluminum construction with a grafal coating applied to the skirt to reduce noise, friction, and scuffing.

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The MINI COOPER pistons have flat tops. The MINI COOPER S has a concave piston top with a volume of 1.66cc to reduce the compression ratio.

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Grafal Coating

Grafal consists of a fine colloidal graphite which is bonded with resin. It is between 10 and 20 micrometers thick (0.010-0.020 mm) and is applied by means of a printing process, followed by curing.

Improved adhesion properties are achieved by a thin metallic phosphate layer or other proven methods which are applied prior to coating.

Oil Pan

The oil pan is constructed of die cast aluminum. It is secured to the support ladder by 13 bolts. The oil pan provides a mounting position for the air conditioning compressor on the right side of the engine (viewed from the crankshaft pulley) and for the engine tie rod bracket on the left side of the engine.

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The seal between the oil pan and bearing ladder has a washer fitted to each bolt location to prevent over tightening and distortion of the seal. A lip on the oil pan seal ensures correct location to the bearing ladder. The insert shows the sealing ribs to prevent oil leakage.

Cylinder Head

The cross flow design cylinder head includes a single overhead camshaft, two rocker shafts and four valves per cylinder. The valves are arranged in two inline banks, the intake side facing towards the radiator, the exhaust facing towards the firewall.

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Cylinder Head Gasket

The head gasket is constructed from three layers of sheet metal and is termed as a "multi layered steel gasket". Four small rivets on the outer edge of the gasket hold the three layers together. The head gasket contains an oil restrictor that controls the oil flow to the cylinder head. This restriction allows a better oil supply to the block.

An oversized gasket is available in case the cylinder or deck have been machined.

The standard thickness of the gasket is .065 mm with a thicker (.095mm) available.

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Workshop Hint

The gasket does not have any markings to indicate the correct orientation of the gasket, this is determined by the location dowels and oil transfer gallery

Workshop Hint

The head bolt should be discarded and a new one installed should there be any evidence of thinning at any point along its length.

Positive Crankcase Ventilation Pipe A.

The PCV valve in the valve cover has Pipe A connecting it to the intake manifold, this connection is downstream of the throttle valve (High vacuum area).

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Positive Crankcase Ventilation Pipe B.

Pipe B connects the valve cover to the intake system rubber bellows between the air cleaner and throttle body, this connection is upstream of the throttle valve. Pipe B has no restrictions and allows air to travel in both directions depending on the pressure in the crankcase.

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Under normal driving conditions (negative crankcase pressure), air is drawn into the crankcase via pipe B and mixes with the blow by gases in the crankcase. The gases pass back up through the crankcase and re-enter the cylinder head cover. A negative pressure (vacuum) in the manifold will be sufficient to open the PCV valve and allow the gases to enter the inlet manifold downstream of the throttle valve through pipe A and be drawn into the combustion chambers.

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When the engine speed is high (positive crankcase pressure), the volume of blow-by gases may be too great for the PCV valve to handle alone, vacuum in the inlet manifold will also be greatly reduced. Under these conditions the blow-by gases will also flow through pipe B and enter the air inlet system upstream of the throttle valve, where they will be drawn into the combustion chambers.

Camshaft

The camshaft on both the W10 and W11 are the same. They are machined from nodular iron. Nodular iron combines many advantages including good castability, excellent machinability, wear resistance, and weight savings.

The camshaft consists of 5 bearing journals and three valve lift lobes per cylinder. The intake side uses one rocker per valve, while on the exhaust side a single rocker operates both valves. A machined recess in the cylinder head next to the Number 5 camshaft journal controls the camshaft end float. Rocker Arms and Rocker Shafts

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The rocker shafts are hollow to allow an oil supply to the hydraulic lifters that are retained in the end of the rocker arm. The valves are opened by roller rocker/hydraulic lifter assemblies, which pivot on the rocker arm shafts.

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Valves

Powder metal valve guides and seats are installed on both engine derivatives, the valves, springs and retainers are of conventional design.

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Intake Valves

The intake valves are made from carbon steel. The carbon content allows the valve to be hardened and tempered to increase strength and also to be locally hardened to improve wear resistance. The MINI COOPER S uses an upgraded material.

Intake Valve Seat Inserts

Powder metal technology is used for valve seat inserts as the sintered part requires little or no machining and any number of material compositions can be developed to satisfy particular engine demands.

Exhaust Valves

The exhaust valve specification is an austenitic steel, a particular type of steel with characteristics that are ideal for exhaust valve manufacture. The MINI COOPER S has upgraded exhaust valves.

Exhaust Valve Seat Inserts

Many of the characteristics for the intake valve seat inserts carry over to the exhaust valve seat inserts. In addition, the exhaust valve seat uses what is known as "Grade J" steel, this contains molybendum and tungsten. This provide high heat hardness giving increased resistance to indentation and wear.

Powder Technology

A shape is produced from powdered metal by filling a rigid die with a blended powder and applying pressure.

The pressure causes the powder particles to be forced together in an interlocking of particles similar to a weld.

After being pressure formed the parts are heated to 80% of the boiling point of the metal. The heat increases the bonds between the particles and further strengthens the part.

To increase thermal conductivity the pores of the powder compact are infiltrated with copper during the sintering process.

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There is a fixed chain guide on the intake side of the engine. The exhaust side has a semi-floating guide that is spring-loaded and contains a self-ratcheting tensioner to retain the adjusted position. Engine oil pressure fine-tunes the free play using a hydraulic tensioner.

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The timing chain incorporates three copper color links that are used to assist timing chain installation. Both the crankshaft and camshaft gears incorporate timing marks, which are used in conjunction with the copper coated chain links.

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Workshop Hint

Before reinstalling the timing chain tensioner the plunger must be placed in the "transit" position. This is achieved by pushing the plunger fully in until it locks in place.

This moves the mechanical ratchet mechanism to the start position. When the tensioner has been installed in the engine, the chain guide is pushed towards the tensioner to release the plunger ratchet mechanism to apply the correct amount of tension to the timing chain.

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A key way locates the crankshaft gear (23 Teeth). The camshaft timing gear (46 Teeth) is located by a key way and is retained by a central bolt. The camshaft gear is driven by a roller timing chain.

Lubrication System

The lubrication system is the full flow filtration pressure feed type. The oil fill process at the factory allows for a tolerance of 4mm above to 4mm below the maximum mark on the oil level dipstick. The oil level will depend on the oil temperature and length of time from the last engine switch off.

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Oil Circuit

Oil is drawn up through the oil strainer to the oil pump, which is located at the front of the engine: the oil pump delivers oil under pressure through the full flow oil filter to the main oil gallery.

The main oil gallery runs the full length of the engine block and delivers oil to the main bearings. Diagonal drillings in the crankshaft webs deliver oil to the connecting rod bearings. The cylinder bores and connecting rod small end are splash lubricated from directed slots on the connecting rod thrust collar.

The main oil gallery also supplies oil to the cylinder head assembly via a vertical hole on the exhaust side of the cylinder block between bores two and three. The cylinder head gasket incorporates an oil restrictor to ensure that oil volume to the crankshaft is maintained and oil volume to the cylinder head is reduced.

Upper engine lubrication is provided by one main feed to the number three camshaft bearing cap. Oil is then routed through the rocker shafts to the remaining camshaft bearing caps and rocker arms/hydraulic lifters.

Oil returning to the sump pan from the pressurized components supplies lubrication to the valve stems.

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Piston Cooling - MINI COOPER S Only

The MINI COOPER S incorporates oil "squirt" jets to assist in the cooling of the piston crown. The four jets are located in the cylinder block next to the main oil gallery. Oil spray is controlled by a ball and spring. These allow oil flow only when the oil pressure exceeds 2 bar. The position of each jet is critical to the effectiveness of the cooling.

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Oil Pump

The oil pump and pressure relief valve are located on the front cover (internally) and are secured by 10 bolts. They are both manufactured from aluminum. The oil pump consists of two gears. The internal gear is driven directly from two flats on the crankshaft nose and is in permanent mesh with the outer gear.

The eccentric rotation of the gears creates a low pressure at the inlet suction crescent end of the pump and draws in oil. As the gearwheel rotates, oil will be compressed between the gears and discharged at the outlet port end of the crescent at a high pressure.

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Oil Pressure Regulator

The oil pressure relief valve is installed in the oil pump housing. The valve consists of a spring, retaining cap, circlip and hollow plunger with radial holes.

If a blockage or restriction occurs and the oil pressure is sufficient to overcome the spring tension, the plunger will be forced back, exposing the radial holes and oil will return to the low pressure side of the pump.

Oil Filter Housing

The oil filter housing is located adjacent to the exhaust manifold and is externally mounted by three bolts.

The housing incorporates a spring-loaded drain back function, allowing oil to return to the oil pan. The drain back function is activated as the oil filter top housing is unscrewed. The oil filter housing also retains a bypass valve for the full flow oil filter and an oil pressure switch. The oil filter is a disposable paper element and is retained in the upper section of the aluminum housing.

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Service Update

It is imperative that the plastic sleeve and spring not be discarded under any circumstances.

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Workshop Hint

When replacing the oil filter element, unscrew the upper housing slowly, This will allow sufficient time for the drain back valve to open and release oil to the sump. Removing the housing quickly could allow oil to overflow onto the suspension.

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MINI COOPER

The MINI COOPER flywheel is constructed from steel and is retained on the crankshaft by eight flanged head bolts. Two dots are used for correct alignment, one on the crankshaft and the other on the flywheel.

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MINI COOPER S

On MINI COOPER S a dual mass flywheel is used to insulate the gearbox from torsional and transient vibrations produced by the engine or drive line. The flywheel consists of a primary and a secondary flywheel. The drive between the two is transferred by a torsional damper made up of four coil springs located in the inside diameter of the primary flywheel. Under high torque loading conditions the secondary flywheel can rotate in either direction up to 70 degrees in relation to the primary flywheel.

Cooling System

Engine cooling on the MINI comes in two forms, although the basic layout remains the same. Both systems use a 50/50 coolant solution with standard kevlar reinforced EPDM (Ethylene Propylene Diene Monomer) cooling hoses.

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Cooling System Operation

When the engine is cold the thermostat is closed, preventing the coolant from circulating through the radiator. Coolant is able to circulate through the heater core, expansion tank, and on the MINI COOPER S, the oil cooler.

The MINI COOPER S has a pressurized expansion tank, and allows coolant to enter the top via the heater core pipe, and exit the bottom of the tank to join the heater core return pipe.

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As the coolant temperature increases the thermostat gradually opens. This allows a bleed of coolant from the bottom hose into the cylinder block via the coolant pump, and allows hot coolant to flow to the radiator via the top hose. The flow of hot and cold coolant is balanced to maintain the optimum engine temperature. When the thermostat opens fully, the full flow of coolant passes through the radiator.

The coolant pump is manufactured from die cast aluminum and is driven by the auxiliary belt on the MINI COOPER. It is installed on the intake side of the engine block (towards the front of the car).

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The MINI COOPER S coolant pump is driven by the supercharger via a reduction gearbox. The coolant pump is fitted directly onto the supercharger housing and is connected by a two legged dog drive (similar to a conventional transmission torque converter)..

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Thermostat

The thermostat is located in the cylinder head and is retained by a plastic housing (aluminum on COOPER S). The thermostat begins to open at 89-92 and is fully open at 103°C. The MINI COOPER thermostat housing also incorporates the cooling system pressure cap (MINI COOPER S system pressure cap is installed on the expansion tank)

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Expansion Tank

The plastic expansion tank for both models is located between the primary and secondary bulkheads. Both models use a pressure cap to pressurize the cooling system to 1.1bar (16 psi) at which point the cap valve will lift to relieve pressure.

The MINI COOPER expansion tank is a non-pressurized type, it is only used to collect excess coolant due to heat expansion, and this coolant will be drawn back into the system as the coolant cools. The MINI COOPER S is fitted with a conventional pressurized cap on the expansion tank.

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Radiator

The radiator installed in the MINI COOPER (COOPER S) is a conventional cross flow type. It is constructed from aluminum tubes, wavy corrugated cooling strips and plastic end caps. Coolant flows from the top left to the bottom right (viewed from the front of the car). There are two radiator arrangements for the MINI COOPER and only one for the COOPER S.

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Heater Core

The heater core is constructed of aluminum and is of conventional design. The coolant passages are not blocked off by shutoff valves. Coolant should always flow through the heater core unless an obstruction is present.

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Coolant Fan

The Coolant Fan is a nine bladed fan measuring 400 mm in diameter, driven by a 350 watt motor and controlled by the EMS 2000. This system has two fan speeds.

Low speed is switched on at 105°C coolant temp and off when the temperature drops to 101°C.

High speed is switched on at 112°C and remains on until the system coolant temperature drops by 4°C at which point the system will revert to Low speed.

The cooling fan will also operate on Low speed when the Air Conditioning is switched on and system pressure reaches 8 bar. Should the Air Conditioning system pressure rise to 18 bar, the fan will automatically run on the High speed.

The cooling fan for the EHPS (electronic hydraulic power steering pump) is run by the same circuit as the main coolant fan. Whenever the coolant fan is running the EHPS fan should also be running.

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Oil Cooler MINI COOPER S

The MINI COOPER S is fitted with a plate type oil cooler mounted directly onto the oil filter housing. Engine oil from the filter housing and coolant from the hoses flows through the cooler tubes adjacent to each other. This process takes place continuously: there is no thermostat control. The inlet and outlet pipes are connected in parallel with the heater core pipes.

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A twin tie bar torque axis system is used on all MINI engine derivatives. The system consists of 2 mass carriers and 2 torque reacting tie bars. Brackets, bolt and mount rates vary with engine/gearbox combinations.

The hydramount and hydrabush carry the mass of the engine. They control the vertical and lateral movements of the engine. These movements are generated by the engine itself and through road inputs from the suspension.

The tie bars control torque reaction. This is the natural fore-aft movement of the engine during acceleration and deceleration.

Hydramount

The hydramount is located on the right hand side of the engine (viewed from the driver seat). It is filled with glycol fluid to absorb vibration. The bracket that is located directly on the mount is constructed from cast aluminum and is attached by four bolts to the top of the cylinder block.

Hydrabush

The Hydrabush is located between a two part assembly mounted on top of the gearbox. It consists of two die cast aluminum housings. The first part is bolted directly on top of the gearbox and houses the hydrabush. The second part is connected from the inner strut housing to the hydrabush. This also provides additional mountings for the fusebox, battery box (MINI COOPER only) and air cleaner assembly.

Top Stabilizer Bar

The stabilizer consists of a large die cast aluminum housing. This is bolted to the rear of the suspension strut and houses a large bushing. A mild steel bracket is used to connect the strut mount to the twin axis mount that incorporates a small bushing, this will be available as a separate part.

Lower Stabilizer Bar

The lower stabilizer is also constructed from die cast aluminum and incorporates two bushings of different sizes. The large bushing is bolted directly on to the subframe crossmember. The other end is fixed to a mild steel bracket, bolted on the sump pan.

Auxiliary Belt

The Auxiliary belt is of six-rib construction. Two different arrangements are available.

The MINI COOPER uses a torsional spring to apply load to the belt and a friction damper to reduce the pulsating vibrations from the engine.

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The MINI COOPER S Spring travel stop uses a compression spring to apply to load to the belt and a hydraulic damper to control the engine pulsation.

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Intercooler (MINI COOPER S only)

Heat exchangers, now more commonly known as intercoolers, were originally used on large diesel engines in conjunction with a blower (supercharger). The intercooler construction is similar to that of the engine radiator.

Advantages of an intercooler.

1. Increases mass/density of air change entering the cylinders.
2. Helps keep cylinder head temperature lower.
3. Reduces oxides of nitrogen.

There are two types of intercooler.

1. Air to liquid intercooler.
2. Air to air intercooler.

MINI COOPER S uses an air to air intercooler. The major advantage of the air to air intercooler over the air to liquid intercooler is its capacity to reduce the temperature of the compressed air charge to around 40-50°C (104-122°F).

Operation

When the compressed air mass leaves the outlet of the supercharger, the molecules of air are tightly packed together which generates heat. The air is forced into the inlet of the intercooler and is passed through many elongated tubes.

The ram air effect takes place as the vehicle moves forward and outside air passes externally over the elongated tubes cooling the compressed charge sufficiently before leaving the intercooler.

Location

The intercooler is located directly on top of the supercharger. It is mounted by 2 top hat brackets at the front, with the rear of the intercooler solidly mounted.

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Supercharger History

The first "Blower" was designed and patented in 1865 by F.M. and P.H. Roots. They were used for various purposes but a popular early application was for mine shaft ventilation.

The first type of Blower used on motor vehicles was a Roots rotating type. This "positive driven" type would consume up to 15% of engine power. On the MINI COOPER S the supercharger will consume a maximum of 20 kW of power (17% of maximum power output).

The decline in the use of positive driven blowers came with demands on motor manufacturers to produce more efficient and smaller engines. Most manufacturers at this time opted for the non positive driven blower known as the turbocharger. This has the advantage of not consuming any engine power directly but was not capable of delivering increased engine power at low engine speeds (turbo lag).

With the advantage of new material and designs the positive driven blowers have once again risen in popularity among motor manufacturers. Over the past few years, design engineers have managed to enhance the operation of the supercharger, now providing the following

1. Increased Power Output.
2. A 40% net increase in power, without affecting fuel economy.
3. Improved Reliability and Life Expectancy.
4. Newly developed 60 degree twisted rotors (helix), aided with high quality bearing seals and synthetic oil (sealed for life).
5. Improved Quietness.
6. Newly developed inlet/outlet ports and ducting mounts.

The MINI COOPER S is fitted with a "state of the art" supercharger that has been specifically engineered for small engines. It was designed as a compact unit with the ability to provide the performance that is synonymous with the COOPER S name.

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Supercharger Operation

The supercharger is a positive displacement pump. Its purpose is to increase air pressure and density in the intake manifold. The supercharger is matched to the engine by its displacement and belt ratio (driven from the crankshaft). The concentrated charge of air provided by the supercharger results in a more powerful combustion stroke in the engine's cylinders, resulting in improved performance over non-supercharged engines.

The supercharger incorporates a specially designed bypass valve. This is actuated by a vacuum pipe near the throttle body and re-circulates the supercharger air when boost is not required. During typical driving conditions the intake manifold is under pressure for only 5% of the time. For the remaining time the intake manifold is under vacuum (negative pressure), allowing for better fuel economy and a quieter ride.

Inside the supercharger the helix angled rotors and specially designed inlet and outlet port geometry reduce pressure variations. This results in a smooth discharge flow and a lower level of noise during operation. The way in which the ducting to and from the supercharger is mounted also plays a major role in reducing noise.

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Exhaust System

The exhaust system on the MINI is constructed in two sections

1. The manifold and front pipe - manufactured as a single piece.
2. The center/rear section - manufactured as a single piece that can include up to three silencers, dependent on the model.

Exhaust Manifold and Front Pipe

The Manifold and front pipe is common to both models. The flange of the front pipe (cylinder head mounting) is manufactured from mild steel, while the four primary tracks are of stainless steel. They all join a load supporting decoupler. From the decoupler the exhaust continues in a single pipe to the metallic starter catalyst and the ceramic catalyst. The outer casing of the catalyst is manufactured from stainless steel. From the catalyst a short section of pipe meets the mounting flange that is joined to the center pipe by a two point mounting. To meet emission legislation an additional oxygen sensor is fitted downstream of the catalyst.

Center Pipe and Rear Silencer.

All tailpipe silencers have an Aluminized mild steel outer casing. The rubber support hangers are silicone based. The system is designed to meet current noise legislation producing just 74 dB.

The MINI COOPER has a silencer located at the front of the center pipe, which has a volume of 1.8 liters. The rear silencer is finished with a polished stainless steel tailpipe trim, known as the "Coke" can design.

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The MINI COOPER S also has a center silencer but its size has been increased to 3 liters. The rear section of the exhaust consists of two silencers; one mounted on each side of the vehicle by two sets of silicone based hangers. Two pipes leave the left hand silencer and exit the body in the center of the vehicle. The tail pipes are finished with polished stainless steel trim.

Driveshafts

The old Mini had an outer constant velocity joint and "Moulton" rubber coupling for the inner joint, this is in fact a combination of rubber and metal. The construction was a metal cross inside rubber bushings encased with steel shells. The coupling was connected to the shaft and differential flange by "U" bolts, two holding it to the shaft, two holding it to the flange. Early Cooper "S" and vehicles with an automatic gearbox had a "Hardy Spicer" universal joint. Horizontal movement of the shaft was by a sliding joint incorporated into the mounting for the coupling. These inner joints later changed to a plunge joint for all models.

Purpose of the System

Much the same as the old Mini, drive on MINI is transmitted through the front steering wheels, consequently the design of these shafts is different to those on rear wheel drive vehicles, as a greater degree of articulation is required on the outer joints. Two different diameters of joints for inner and outer are used. The larger size is for the MINI COOPER S and the smaller for MINI COOPER with R65 or ECVT gearboxes.

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Primary components of the Driveshaft System include

1. Driveshafts Left and Right Side
2. Intermediate Shaft Right Side Only
3. Support Bearing
4. Outer Joints
5. Inner Joints
6. Front Hubs

DRIVE SHAFT BAR

System Components

The drive train for all three gearboxes consists of the same elements. A final drive, offset to the left of the center line of the vehicle by varying amounts. An intermediate shaft connects to the right hand side of the final drive with a support bearing at its outer end. The support bearing is fixed by a bracket and bolts to the engine block lower and ladder rail and incorporates the inner joint. This configuration in effect gives two drive shafts of equal length. The benefit of this is to reduce drive shaft derived torque steer that can be a problem on front wheel drive cars with un-equal length drive shafts.

Driveshaft Bar Shafts

The inner and outer joints are connected together by bar-shafts of solid construction but different lengths and diameters depending on the gearbox used. All outer joints have shields to protect the wheel speed sensors. ECVT and R65 have shields on the inner joints to protect the drive shaft seal. The MINI COOPER S has no need for a shield on the left hand inner joint due to the proximity of the inner joint to the differential housing.

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Outer Joints

To achieve greater articulation the outer joint has six ball bearings located in a cage running on convex grooves on the inner race and longitudinal elliptical grooves in the outer joint.

The outer joint construction allows the joint to turn at the same speed as the shaft when in line and when the joint is turned through any position up to 45°. The name for this type of joint is "constant velocity". This design applies to the outer joints on all models.

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Inner Joints

The inner joint is of the tripod type with spherical bearings to reduce sliding resistance. The joint has three bearings supported on needle roller bearings. This allows the shaft to slide horizontally inside the joint. The horizontal sliding movement will allow the overall length (differential to hub) of the shaft to increase or decrease as required with suspension travel.

A maximum drive angle of 25° is possible with this type of joint but the working angle is normally less than 10°. This is why tripod plunge joints are normally positioned at the differential end of the drive shaft.

On the left hand inner joint, used with the R65 gearbox, the drive shaft it is retained in the differential by pressure from a spring located between the two halves of the inner joint.

On ECVT and Getrag the left hand drive shaft is located in the differential by a spring ring on the end of splines.

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Front Hub

The front hub is a unitary construction with the wheel flange. The flange acts as the outer race of the outer bearing and is machined to take the outer race of the inner bearing. This hub bearing is of the ball type. The drive shaft is located onto the wheel bearings with multi-splines, and retained by a lock nut. The tightening of the nut provides the correct amount of pre-load on the wheel bearings.

Repair Information

Two different types of lubrication are used for the drive shaft joints. The outer joint uses a graphite-based grease and the inner joint uses high temperature melting point grease.

Drive shaft boots (inner and outer) are available to replace separately in the event of a split or damaged boot. The appropriate type of grease is supplied with the boot kit.

A BMW Special Tool will be available to aid the removal of the left hand drive shaft inner joint from the differential on the MINI COOPER with ECVT and the MINI COOPER S.